sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: white/cream/light gray; Luster: waxy to dull; Breakage: conchoidal fracture (smooth, shell-like curves); Crystal structure: Microcrystalline (cryptocrystalline) quartz.

Hardness: 7 on Mohs scale
Color: white/cream/light gray
Luster: waxy to dull

Identified July 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids within other sedimentary rocks like limestone or dolomite.

Uses & applications

Historically used for making stone tools (arrowheads, knives) due to its sharp edges; used in construction aggregate and as a spark-generator in flintlock firearms.

Geological facts

Because it breaks with a conchoidal fracture, it produces edges that are sharper than a steel scalpel. It is remarkably resistant to chemical weathering and often remains as nodules in soil after the surrounding bedrock has weathered away.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and characteristic shell-like curved breaks. It often feels smoother than the rocks surrounding it.